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A059086 Number of labeled T_0-hypergraphs with n distinct hyperedges (empty hyperedge included). 7
2, 5, 30, 18236, 2369751620679, 5960531437867327674541054610203768, 479047836152505670895481842190009123676957243077039693903470634823732317120870101036348 (list; graph; refs; listen; history; text; internal format)
OFFSET
0,1
COMMENTS
A hypergraph is a T_0 hypergraph if for every two distinct nodes there exists a hyperedge containing one but not the other node.
LINKS
FORMULA
a(n) = (1/n!)*Sum_{k = 0..n} stirling1(n, k)*floor((2^k)!*exp(1)).
EXAMPLE
a(2)=30; There are 30 labeled T_0-hypergraphs with 2 distinct hyperedges (empty hyperedge included): 1 1-node hypergraph, 5 2-node hypergraphs, 12 3-node hypergraphs and 12 4-node hypergraphs.
a(3) = (1/3!)*(2*[2!*e]-3*[4!*e]+[8!*e]) = (1/3!)*(2*5-3*65+109601) = 18236, where [k!*e] := floor (k!*exp(1)).
MAPLE
with(combinat): Digits := 1000: for n from 0 to 8 do printf(`%d, `, (1/n!)*sum(stirling1(n, k)*floor((2^k)!*exp(1)), k=0..n)) od:
CROSSREFS
Column sums of A059084.
Sequence in context: A275255 A219273 A000133 * A363243 A215168 A370830
KEYWORD
easy,nonn
AUTHOR
Goran Kilibarda, Vladeta Jovovic, Dec 27 2000
EXTENSIONS
More terms from James A. Sellers, Jan 24 2001
STATUS
approved

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Last modified April 24 11:49 EDT 2024. Contains 371936 sequences. (Running on oeis4.)